1. Technical Field
The present invention relates to a base station, terminal, band assignment method and downlink data communication method.
2. Description of the Related Art
In 3GPP LTE, OFDMA (Orthogonal Frequency Division Multiple Access) is adopted as a downlink communication scheme. In a radio communication system adopting 3GPP LTE, a radio communication base station apparatus (which may be simply referred to as “base station” below) transmits a synchronization channel (“SCH”) or broadcast channel (“BCH”) using predetermined communication resources. Then, first, a radio communication terminal apparatus (which may be simply referred to as “terminal” below) secures synchronization with the base station by capturing the SCH. That is, first, the terminal performs a cell search. After that, the terminal obtains parameters unique to the base station (such as a frequency bandwidth) by reading the BCH information (see Non-Patent Literatures 1, 2 and 3).
Also, standardization of 3GPP LTE-advanced, which realizes faster communication than 3GPP LTE, has been started. The 3GPP LTE-advanced system (which may be referred to as “LTE+ system” below) follows the 3GPP LTE system (which may be referred to as “LTE system” below). In 3GPP LTE-advanced, to realize downlink transmission speed equal to or greater than maximum 1 Gbps, it is expected to adopt a base station and terminal that can perform communication in a wideband frequency equal to or greater than 20 MHz. Here, to prevent unnecessary complication of the terminal, the terminal side is expected to define the terminal capability related to frequency band support. The terminal capability defines that, for example, the minimum value of support bandwidth is 20 MHz.
That is, a base station supporting the LTE+ system (which may be referred to as “LTE+ base station” below) is formed to be able to perform communication in a frequency band including a plurality of “unit bands.” Here, a “unit band” is a band of a 20-MHz range, including SCH (Synchronization CHannel) near the center, and is defined as a base unit of a communication band. Also, a “unit band” may be expressed as “component carrier(s)” in English in 3GPP LTE.
Also, terminals supporting the LTE+ system (which may be referred to as “LTE+ terminal” below) include a terminal in which a communication-capable bandwidth can contain only one unit band (which may be referred to as “type-1 LTE+ terminal” below) and a terminal in which a communication-capable bandwidth can contain a plurality of unit bands (which may be referred to as “type-2 LTE+ terminal” below).